Methods of using lost circulation compositions

ABSTRACT

A method of servicing a wellbore in contact with a subterranean formation, comprising: placing a wellbore servicing fluid comprising a crosslinkable polymer system and a filler into a lost circulation zone within the wellbore. A method of blocking the flow of fluid through a lost circulation zone in a subterranean formation comprising placing a first composition comprising a packing agent into the lost circulation zone, placing a second composition comprising a crosslinkable polymer system and a filler into the lost circulation zone, and allowing the compositions to set into place.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure relates to compositions for servicing a wellboreexperiencing lost circulation. More specifically, this disclosurerelates to introducing compositions into a wellbore penetrating asubterranean formation to reduce the loss of fluid to the formation.

2. Background of the Invention

A natural resource such as oil or gas residing in a subterraneanformation can be recovered by drilling a well into the formation. Thesubterranean formation is usually isolated from other formations using atechnique known as well cementing. In particular, a wellbore istypically drilled down to the subterranean formation while circulating adrilling fluid through the wellbore. After the drilling is terminated, astring of pipe, e.g., casing, is run in the wellbore. Primary cementingis then usually performed whereby a cement slurry is pumped down throughthe string of pipe and into the annulus between the string of pipe andthe walls of the wellbore to allow the cement slurry to set into animpermeable cement column and thereby seal the annulus. Subsequentsecondary cementing operations, i.e., any cementing operation after theprimary cementing operation, may also be performed. One example of asecondary cementing operation is squeeze cementing whereby a cementslurry is forced under pressure to areas of lost integrity in theannulus to seal off those areas.

Subsequently, oil or gas residing in the subterranean formation may berecovered by driving the fluid into the well using, for example, apressure gradient that exists between the formation and the wellbore,the force of gravity, displacement of the fluid using a pump or theforce of another fluid injected into the well or an adjacent well. Theproduction of the fluid in the formation may be increased byhydraulically fracturing the formation. That is, a viscous fracturingfluid may pumped down the casing to the formation at a rate and apressure sufficient to form fractures that extend into the formation,providing additional pathways through which the oil or gas can flow tothe well. Unfortunately, water rather than oil or gas may eventually beproduced by the formation through the fractures therein. To provide forthe production of more oil or gas, a fracturing fluid may again bepumped into the formation to form additional fractures therein. However,the previously used fractures first must be plugged to prevent the lossof the fracturing fluid into the formation via those fractures.

In addition to the fracturing fluid, other fluids used in servicing awellbore may also be lost to the subterranean formation whilecirculating the fluids in the wellbore. In particular, the fluids mayenter the subterranean formation via depleted zones, zones of relativelylow pressure, lost circulation zones having naturally occurringfractures, weak zones having fracture gradients exceeded by thehydrostatic pressure of the drilling fluid, and so forth. As a result,the service provided by such fluid is more difficult to achieve. Forexample, a drilling fluid may be lost to the formation, resulting in thecirculation of the fluid in the wellbore being too low to allow forfurther drilling of the wellbore. Also, a secondary cement/sealantcomposition may be lost to the formation as it is being placed in thewellbore, thereby rendering the secondary operation ineffective inmaintaining isolation of the formation.

Accordingly, an ongoing need exists for compositions and methods ofblocking the flow of fluid through lost circulation zones insubterranean formations.

BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS

Disclosed herein is a method of servicing a wellbore in contact with asubterranean formation, comprising: placing a wellbore servicing fluidcomprising a crosslinkable polymer system and a filler into a lostcirculation zone within the wellbore.

Further disclosed herein is a method of blocking the flow of fluidthrough a lost circulation zone in a subterranean formation comprisingplacing a first composition comprising a packing agent into the lostcirculation zone, placing a second composition comprising acrosslinkable polymer system and a filler into the lost circulationzone, and allowing the compositions to set into place.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 is a graph of a thickening time test.

FIGS. 2-5 are graphs of a static gel strength test.

FIG. 6 is a graph of predicted versus observed static gel strength.

FIGS. 7-11 are pictures of a lost circulation composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed herein are lost circulation compositions (LCC) which may beused to block the flow of fluid through lost circulation zones in asubterranean formation. The LCC may comprise a crosslinkable polymersystem and a filler. Alternatively, the LCC may comprise a crosslinkablepolymer system, a filler and a packing agent. LCCs such as thosedisclosed herein may be used to block the flow of fluid through pathwayssuch as fractures filled with water, voids or cracks in the cementcolumn and the casing, and so forth. Additionally, LCCs such as thosedisclosed herein may be used to improve wellbore pressure containmentability when introduced to areas of lost circulation.

In an embodiment, the LCC comprises a crosslinkable polymer system.Examples of suitable crosslinkable polymer systems include, but are notlimited to, the following: a water soluble copolymer of a non-acidicethylenically unsaturated polar monomer and a copolymerizableethylenically unsaturated ester; a terpolymer or tetrapolymer of anethylenically unsaturated polar monomer, an ethylenically unsaturatedester, and a monomer selected from acrylamide-2-methylpropane sulfonicacid, N-vinylpyrrolidone, or both; or combinations thereof. Thecopolymer may contain from one to three polar monomers and from one tothree unsaturated esters. The crosslinkable polymer system may alsoinclude at least one crosslinking agent, which is herein defined as amaterial that is capable of crosslinking such copolymers to form a gel.As used herein, a gel is defined as a crosslinked polymer networkswollen in a liquid medium. The crosslinking agent may be, for exampleand without limitation, an organic crosslinking agent such as apolyalkyleneimine, a polyfunctional aliphatic amine such aspolyalkylenepolyamine, an aralkylamine, a heteroaralkylamine, orcombinations thereof. Examples of suitable polyalkyleneimines includewithout limitation polymerized ethyleneimine and propyleneimine.Examples of suitable polyalkylenepolyamines include without limitationpolyethylene- and polypropylene-polyamines. A description of suchcopolymers and crosslinking agents can be found in U.S. Pat. Nos.5,836,392; 6,192,986, and 6,196,317, each of which is incorporated byreference herein in its entirety.

The ethylenically unsaturated esters used in the crosslinkable polymersystem may be formed from a hydroxyl compound and an ethylenicallyunsaturated carboxylic acid selected from the group consisting ofacrylic, methacrylic, crotonic, and cinnamic acids. The ethylenicallyunsaturated group may be in the alpha-beta or beta-gamma positionrelative to the carboxyl group, but it may be at a further distance. Inan embodiment, the hydroxyl compound is an alcohol generally representedby the formula ROH, wherein R is an alkyl, alkenyl, cycloalkyl, aryl,arylalkyl, aromatic, or heterocyclic group that may be substituted withone or more of a hydroxyl, ether, and thioether group. The substituentcan be on the same carbon atom of the R group that is bonded to thehydroxyl group in the hydroxyl compound. The hydroxyl compound may be aprimary, secondary, iso, or tertiary compound. In an embodiment, atertiary carbon atom is bonded to the hydroxyl group, e.g., t-butyl andtrityl. In an embodiment, the ethylenically unsaturated ester is t-butylacrylate.

The non-acidic ethylenically unsaturated polar monomers used in thecrosslinkable polymer system can be amides, e.g., primary, secondary,and/or tertiary amides, of an unsaturated carboxylic acid. Such amidesmay be derived from ammonia, or a primary or secondary alkylamine, whichmay be optionally substituted by at least one hydroxyl group as inalkylol amides such as ethanolamides. Examples of such carboxylicderived ethylenically unsaturated polar monomers include withoutlimitation acrylamide, methacrylamide, and acrylic ethanol amide.

In an embodiment, the crosslinkable polymer system is a copolymer ofacrylamide and t-butyl acrylate, and the crosslinking agent ispolyethylene imine. These materials are commercially available as theH₂ZERO service providing conformance control system from HalliburtonEnergy Services. The H₂ZERO service providing conformance control systemis a combination of HZ-10 polymer and HZ-20 crosslinker. HZ- 10 is a lowmolecular weight polymer consisting of polyacrylamide and an acrylateester. The gelation rate of the H₂ZERO service providing conformancecontrol system is controlled by the unmasking of crosslinking sites onthe HZ-20 polymer which is a polyethylene imine crosslinker.

The concentrations of both HZ-10 polymer and HZ-20 crosslinkercontribute to the LCC reaction time, its final mechanical properties andstability. In an embodiment, the crosslinkable polymer system forms aviscous gel in from about 60 mins to about 300 mins, alternatively infrom about 60 mins to about 300 mins at a temperature of from about 180°F. to about 320° F., alternatively from about 180° F. to about 225° F.and, alternatively from about 250° F. to about 320° F. The relativeamounts of HZ-10 polymer and HZ-20 crosslinker suitable for use in thepreparation of LCCs of this disclosure will be described in detail laterherein.

In an embodiment, the LCC comprises a filler. Herein a filler refers toparticulates, also termed finer filler material, designed to bridge offacross the packing agent of the LCC. Such fillers may be smaller in sizethan the packing agent. Details of the filler and packing agent sizewill be disclosed later herein. Such fillers may have a pH of from about3 to about 10. In an embodiment, the filler has a specific gravity ofless than about 1 to about 5, alternatively from about 1.5 to about 5,alternatively from about 1.75 to about 4. Without wishing to be limitedby theory, fillers having a specific gravity in the disclosed range mayproduce a LCC with greater flexibility and ductility.

Examples of suitable fillers include without limitation alkyl quaternaryammonium montmorillonite, bentonite, zeolites, barite, fly ash, calciumsulfate, and combinations thereof. In an embodiment the filler is analkyl quarternary ammonium montmorillonite. In an embodiment, the filleris a water swellable or hydratable clay. In an alternative embodiment,the filler is an oil-based sealing composition that may comprise ahydratable polymer, an organophillic clay and a water swellable clay.Such oil-based sealing compositions are disclosed in U.S. Pat. Nos.5,913,364; 6,167,967; 6,258,757, and 6,762,156, each of which isincorporated by reference herein in its entirety. In an embodiment, thefiller material is FLEXPLUG lost circulation material, which is anoil-based sealing composition comprising alkyl quaternary ammoniummontmorillonite commercially available from Halliburton Energy Services.

In an embodiment, the LCC optionally comprises a packing agent. Examplesof packing agents include without limitation resilient materials such asgraphite; fibrous materials such as cedar bark, shredded cane stalks andmineral fiber; flaky materials such as mica flakes and pieces of plasticor cellophane sheeting; and granular materials such as ground and sizedlimestone or marble, wood, nut hulls, formica, corncobs, gravel andcotton hulls. In an embodiment, the packing agent is a resilientgraphite such as STEELSEAL or STEELSEAL FINE lost circulation additiveswhich are dual composition graphite derivatives commercially availablefrom Baroid Industrial Drilling Products, a Halliburton Energy Servicescompany.

In another embodiment, the packing agent is a resin-coated particulate.Examples of suitable resin-coated particulates include withoutlimitation resin-coated ground marble, resin-coated limestone, andresin-coated sand. In an embodiment, the packing agent is a resin-coatedsand. The sand may be graded sand that is sized based on a knowledge ofthe size of the lost circulation zone. The graded sand may have aparticle size in the range of from about 10 to about 70 mesh, U.S. SieveSeries. The graded sand can be coated with a curable resin, a tackifyingagent or mixtures thereof. The hardenable resin compositions useful forcoating sand and consolidating it into a hard fluid permeable massgenerally comprise a hardenable organic resin and a resin-to-sandcoupling agent. Such resin compositions are well known to those skilledin the art, as is their use for consolidating sand into hard fluidpermeable masses. A number of such compositions are described in detailin U.S. Pat. Nos. 4,042,032, 4,070,865, 4,829,100, 5,058,676 and5,128,390 each of which is incorporated herein by reference in itsentirety. Methods and conditions for the production and use of suchresin coated particulates are disclosed in U.S. Pat. Nos. 6,755,245;6,866,099; 6,776,236; 6,742,590; 6,446,722, and 6,427,775, each of whichis incorporated herein by reference in its entirety. An example of aresin suitable for coating the particulate includes without limitationSANDWEDGE NT conductivity enhancement system that is a resin coatingcommercially available from Halliburton Energy Services.

In some embodiments, additives may be included in the LCC for improvingor changing the properties thereof. Examples of such additives includebut are not limited to salts, accelerants, surfactants, set retarders,defoamers, settling prevention agents, weighting materials, dispersants,vitrified shale, formation conditioning agents, or combinations thereof.Other mechanical property modifying additives, for example, are carbonfibers, glass fibers, metal fibers, minerals fibers, and the like whichcan be added to further modify the mechanical properties. Theseadditives may be included singularly or in combination. Methods forintroducing these additives and their effective amounts are known to oneof ordinary skill in the art.

In an embodiment, the LCC includes a sufficient amount of water to forma pumpable slurry. The water may be fresh water or salt water, e.g., anunsaturated aqueous salt solution or a saturated aqueous salt solutionsuch as brine or seawater.

In an embodiment, the LCC comprises a crosslinkable polymer system and afiller. In such an embodiment, the crosslinkable polymer system may bepresent in an amount of from about 35% to about 90% by volume, and thefiller may be present in an amount of from about 8% to about 40% byvolume.

Alternatively, the LCC comprises a crosslinkable polymer system, afiller and a packing agent. In such an embodiment, the crosslinkablepolymer system may be present in an amount of from about 30% to about90% by volume, the filler may be present in an amount of from about 8%to about 40% by volume, and the packing agent may be present in anamount of from about 1% to about 10% by volume.

The components of the LCC may be combined in any order desired by theuser to form a slurry that may then be placed into a wellboreexperiencing lost circulation. The components of the LCC may be combinedusing any mixing device compatible with the composition, for example abulk mixer. In an embodiment, the components of the LCC are combined atthe site of the wellbore experiencing lost-circulation. Alternatively,the components of the LCC are combined off-site and then later used atthe site of the wellbore experiencing lost circulation. Methods for thepreparation of a LCC slurry are known to one of ordinary skill in theart.

In an embodiment an LCC is prepared by combining the crosslinkablepolymer system H₂ZERO service providing conformance control system witha filler, FLEXPLUG OBM lost circulation material. In such an embodiment,the LCC is prepared by combining from about 35% to about 90% by volumeH₂ZERO service providing conformance control system with from about 8%to about 40% by volume FLEXPLUG OBM lost circulation material.

The H₂ZERO service providing conformance control system is prepared bymixing the HZ-10 low molecular weight polymer consisting ofpolyacrylamide and an acrylate ester with the HZ-20 polyethylene iminecrosslinker. The relative amounts of HZ-10 and HZ-20 to be used in thepreparation of H₂ZERO can be adjusted to provide gelling within aspecified time frame based on reaction conditions such as temperatureand pH. For example, the amount of HZ-20 crosslinker necessary forgelling is inversely proportional to temperature wherein higher amountsof HZ-20 are required at lower temperatures to effect formation of aviscous gel. Additionally, gel time can be adjusted to compensate forthe pH of the filler material. Adjustment of the H₂ZERO serviceproviding conformance control system to provide optimum gelling as afunction of temperature and/or pH is known to one of ordinary skill inthe art. The filler, FLEXPLUG OBM lost circulation material is anoil-based sealing composition comprising alkyl quaternary ammoniummontmorillonite. Without wishing to be limited by theory, such oil-basedsealing compositions may function by the hydratable polymer reactingwith water in the well bore to immediately hydrate and form a highlyviscous gel. The water swellable clay then immediately swells in thepresence of water and together with the viscous gel forms a highlyviscous sealing mass. The organophillic clay may then react with an oilcarrier fluid to add viscosity to the composition so that the polymerand clay do not settle out of the oil prior to reacting with water inthe well bore.

In an embodiment, the LCCs of this disclosure when placed in a lostcirculation zone produce a permanent plug that is flexible, adhesive andof appreciable compressive strength. In an embodiment, the LCCs of thisdisclosure have an appreciable static gel strength (SGS).

The LCCs disclosed herein may be used as wellbore servicing fluids. Asused herein, a “servicing fluid” refers to a fluid used to drill,complete, work over, fracture, repair, or in any way prepare a wellborefor the recovery of materials residing in a subterranean formationpenetrated by the wellbore. Examples of servicing fluids include, butare not limited to, cement slurries, drilling fluids or muds, spacerfluids, fracturing fluids or completion fluids, all of which are wellknown in the art. The servicing fluid is for use in a wellbore thatpenetrates a subterranean formation. It is to be understood that“subterranean formation” encompasses both areas below exposed earth andareas below earth covered by water such as ocean or fresh water.

The LCCs may be introduced to the wellbore to prevent the loss ofaqueous or non-aqueous drilling fluids into lost circulation zones suchas voids, vugular zones, and natural or induced fractures whiledrilling. In an embodiment, the LCC is placed into a wellbore as asingle stream and activated by downhole conditions to form a barrierthat substantially seals lost circulation zones. In such an embodiment,the LCC may be placed downhole through the drill bit forming acomposition that substantially eliminates the lost circulation. In yetanother embodiment, the LCC is formed downhole by the mixing of a firststream comprising one or more LCC components and a second streamcomprising additional LCC components. For example, the LCC may be formeddownhole by the mixing of a first stream comprising a packing agent anda second stream comprising a crosslinkable polymer system and a filler.Methods for introducing compositions into a wellbore to sealsubterranean zones are described in U.S. Pat. Nos. 5,913,364; 6,167,967;and 6,258,757, each of which is incorporated by reference herein in itsentirety.

The LCC may form a non-flowing, intact mass inside the lost circulationzone which plugs the zone and inhibits loss of subsequently pumpeddrilling fluid, which allows for further drilling. It is to beunderstood that it may be desired to hasten the viscosification reactionfor swift plugging of the voids. Alternatively, it may be desired toprolong or delay the viscosification for deeper penetration into thevoids. For example the LCC may form a mass that plugs the zone atelevated temperatures, such as those found at higher depths within awellbore.

In an embodiment, the LCCs may be employed in well completion operationssuch as primary and secondary cementing operations. The LCC may beplaced into an annulus of the wellbore and allowed to set such that itisolates the subterranean formation from a different portion of thewellbore. The LCC thus forms a barrier that prevents fluids in thatsubterranean formation from migrating into other subterraneanformations. In an embodiment, the wellbore in which the LCC ispositioned belongs to a multilateral wellbore configuration. It is to beunderstood that a multilateral wellbore configuration includes at leasttwo principal wellbores connected by one or more ancillary wellbores.

In secondary cementing, often referred to as squeeze cementing, the LCCmay be strategically positioned in the wellbore to plug a void or crackin the conduit, to plug a void or crack in the hardened sealant (e.g.,cement sheath) residing in the annulus, to plug a relatively smallopening known as a microannulus between the hardened sealant and theconduit, and so forth. Various procedures that may be followed to use asealant composition in a wellbore are described in U.S. Pat. Nos.5,346,012 and 5,588,488, which are incorporated by reference herein intheir entirety.

In other embodiments, additives are also pumped into the wellbore withLCC. For example and without limitation, fluid absorbing materials,resins, aqueous superabsorbers, viscosifying agents, suspending agents,dispersing agents, or combinations thereof can be pumped in the streamwith the LCCs disclosed.

The LCCs of this disclosure may provide lost circulation control in asufficiently short time period to prevent the operator from pulling outof the hole and thus reducing nonproductive rig time. Without wishing tobe limited by theory, the packing agent may immediately pack off intothe lost circulation zones in the subterranean formation. The filler maythen squeeze into the lost circulation zones forming a bridge betweenthe larger sized packing agent. Finally, the thermally activatedcrosslinkable polymer system may gel into place to produce a permanentplug that is flexible, adhesive and of appreciable compressive strength.In addition, due to the filler within the slurry the amount ofcrosslinkable polymer system squeezed into the matrix of the surroundingrock may be minimized thus providing a finite layer of rock adjacent tothe plug that has negligible permeability and avoids formation damage.

EXAMPLES

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification of the claims in any manner.

Comparative Example

The ability of H₂ZERO service providing conformance control system toproduce a suitable LCC was evaluated. H₂ZERO service providingconformance control system is a crosslinkable polymer systemcommercially available from Halliburton Energy Services. An H₂ZEROservice providing conformance control system slurry was designed fortemperatures in the range of 120° F. to 190° F., which contained anextremely high percent of HZ-20, Table 1. TABLE 1 Component Percent ofSlurry Weight HZ-10 35.5% HZ-20 48.2% Water 16.3%

Two samples of the base H₂ZERO service providing conformance controlsystem product were mixed and placed in a water bath at 130° F.overnight to confirm the recipe would gel within a reasonable time atthe lower temperature. Both samples made a clear ringing gel that wasstrong but did not hold up to impact and did not exhibit qualitativelydetectable flexibility. Further, when the product was over-stressed itsfailure mode was akin to bursting. The product easily broke apart.

Example 1

The ability of H₂ZERO service providing conformance control system toform an LCC with FLEXPLUG OBM lost circulation material was evaluated.FLEXPLUG OBM lost circulation material is an oil-based sealingcomposition commercially available from Halliburton Energy Services. TheH₂ZERO service providing conformance control system had an adverseeffect on the latex contained within the FLEXPLUG OBM lost circulationmaterial slurry. The FLEXPLUG OBM lost circulation material was thenused as a drymix filler in the H₂ZERO service providing conformancecontrol system slurry. A 9.3 ppg slurry was targeted as this is thedensity of the typical FLEXPLUG OBM lost circulation material slurry.Table 2 lists the components and amounts used to design theH₂ZERO/FLEXPLUG OBM slurry. TABLE 2 Component Percent of Slurry WeightWater 6.9% HZ-10 15.0% HZ-20 59.3% FLEXPLUG OBM 18.9% Drymix lostcirculation material

The samples were heated overnight in a water bath at 130° F. The finalgelled product was much different than the gelled product of the baseH₂ZERO service providing conformance control system described in theComparative Example. The H₂ZERO/FLEXPLUG OBM gelled product exhibitsgreat flexibility, increased toughness, improved resilience andincreased durability to impact. In addition, the H₂ZERO/FLEXPLUG OBMgelled product remained “tacky” unlike the original H₂ZERO serviceproviding conformance control system gelled product.

The above slurry was then tested for pumpability in an HPHTConsistometer at a constant pressure of 1000 psi. The temperature wasprogrammed to initiate the test at 80° F., ramp to 130° F. over aone-hour period, and then ramp to 190° F. over a two-hour period. Table3 contains the consistency readings from this test which is also graphedin FIG. 1. TABLE 3 Test Time (hh:mm) Test Temperature (° F.) Consistency(Bc)¹ 0:00 80 30 3:09 190 70 3:43 190 100¹Bearden consistencyTypically, a fluid is considered “non-pumpable” once it exceeds 70 Bc.The results demonstrate that the compositions remain pumpable until theyreach the desired temperature at which point they rapidly form a highlyflexible, durable and adhesive product.

Example 2

A slurry was prepared as described in Example 1 and the SGS determinedas a function of temperature. The static gel strength development testrequires specialized equipment, such as the MACS Analyzer or theMINIMACS Analyzer. This equipment measures the shear resistance of aslurry under downhole temperature and pressure while the slurry remainsessentially static. The test is conducted by mixing the slurry andplacing into the specialized testing device. The slurry is then stirredand heated to a bottomhole circulating temperature (BHCT) and downholepressure according to the same schedule as the thickening time test.After the slurry reaches the BHCT, stirring is stopped and the slurry isallowed to essentially remain static. The stirring paddle is rotated ata rate of about 0.5°/min while the shear resistance on the paddle ismeasured. The shear resistance is correlated to the SGS (units arelbf/100 ft²) and a plot of SGS development is made as a function oftime.

FIG. 2 is a graph of the results of an SGS test conducted at 80° F.,FIG. 3 is a graph of results of an SGS test conducted at 130° F.; FIG. 4is a graph of results of an SGS test conducted at 160° F., and FIG. 5 isa graph of results from an SGS test conducted at 190° F. The resultsdemonstrate the formation of static gel strength more rapidly atincreased temperatures.

Example 3

An additional H₂ZERO/FLEXPLUG OBM formulation was prepared according toTable 4. TABLE 4 Component Volume (cc) Tap Water 47 HZ-10 97 HZ-20 38FLEXPLUG OBM 74 Drymix lost circulation material (129 g)

The materials in Table 4 were mixed in a MINIMACS for 25 minutes at 1000psi until it reached the preset temperature of 80° F., 130° F., 160° F.or 190° F. Then the MINIMACS set static at t=30 minutes and SGS (lbf/100sq. ft.) recorded v. time. Four tests were conducted, one at each of thetemperatures given. Raw SGS data are given in Table 5. Analysis of thedata revealed the need to model SGS as a function of a “shifted time”defined as follows:Shifted time=t−t _(offset,T)  (1)

Where: t=time of mixing, with t=0 materials added to mixing container;t=30 min went to static conditions; and t_(offset,T)=offset time (min)at the set point temperature of T (F). The room temperature (80° F.)tests never exceeded 40 lbf/100 sq.ft., thus indicating that someinitial minimum temperature is required to initiate the kineticreaction(s) that produce the Theological changes resulting insubstantial gel strength. It is assumed that SGS is a direct indicatorof yield point of the LCC.

FIG. 6 contains the SGS vs time data for the 130° F., 160° F. and 190°F. samples along with the prediction fit of the generalized model in Eq(2).SGS=(t−t _(offset,T))^(α) ^(T)   (2)

where: α_(T) is the “psuedo reaction rate constant” which is a functionof temperature. TABLE 5 Static Gel Strength, Time SGS, (lbf./100 sq.ft.)(mins.) 130° F. 160° F. 190° F. 154 1 160 30 166 50 170 70 177 100 185125 190 150 194 200 200 233 205 275 210 325 214 350 220 395 227 450 230470 235 515 390 1 420 5 480 20 540 35 570 75 600 160 630 290 660 410 690470 100 1 105 8 110 22 115 50 120 82 130 190 140 295 150 410 155 475

TABLE 6 Parameters: t_(offset,T) Time To Reach Temp (F.) α_(T) (min) SGS= 500 (min) 130 1.2 520 710 160 1.43 153 230 190 1.53 99 160

The results demonstrate that deploying the “time shift” concept resultedin a simple but very accurate model for all three temperatures tested.Best-fit values of the parameters in Eq (2) are given in Table 6. Notehow the reaction rate exponent, α_(T), is a function of temperature, aswell as the “time shift” parameter t_(offset,T). Also given in Table 6is the “time to reach SGS=500 lbf/100 sq.ft., ” and note its sensitivityto temperature as well.

Example 4

Preliminary measurements of the mechanical properties of theH₂ZERO/FLEXPLUG OBM gelled product were conducted. For the base slurryrecipe given in Tables 2 and 4, rudimentary testing for the purpose ofcapturing gross compressive strength estimates and visual depictions offlexibility and resilience were performed on three samples of theresultant product. These tests were performed by placing the samples ona Tinius-Olsen machine and gradually increasing the compressive load,while measuring the change in height. The Tinius-Olsen machine is usedto test compressive strength. The compressive load was increased untilthe sample exhibited failure in the form of permanent tears in the axialdirection. Resilience was exhibited by the product returning to near itsoriginal height and diameter when loads were released. In all threecases, the sample returned to its original shape until the point offailure. As can be seen by the photographs taken of one failed sample inFIG. 11, even at this time the sample returns to near its originalshape.

FIG. 7 shows a sample with original dimensions of 3 inch diameter and 2inch height with a 50 lb compressive load applied. The sample, underthis load, had deformed to a height of approximately 1 inch and adiameter of approximately 4¼ inches. FIG. 8 shows this same sample undera 100 lb compressive load. The sample, under this load, had deformed toa height of approximately 1 /2 inch and a diameter of approximately 6inches. FIG. 9 shows this same sample after the 100 lb load has beenremoved. The sample has returned to its original dimensions and shapewith no discernible permanent deformation. A similar result was obtainedwhen the sample was subjected to a 150 lb compressive load (not shown).FIG. 10 shows this same sample under a 200 lb compressive load. As canbe seen by the presence of cracks along the diameter of the specimen,the sample has now failed. Since failure detection was purely throughvisual confirmation, it can only be stated the specimen failed between150 and 200 lbs of compressive force. FIG. 11 shows the failed sampleafter it is taken from the Tinius-Olsen. As can be seen in thisphotograph, the sample returns to near its original shape even after the“starburst” shaped rupture.

Example 5

The compression tests described in Example 4 were repeated with twosmaller samples with a height of 1 inch and a diameter of 2 inches. Theresults were similar to those seen with the larger sample. In general,all three tests showed that a sample can be deformed to approximately27% of its original height and 2 times it original diameter before therepeatable starburst rupture failure occurs. Failure appears to bedependent more on the limitations of deformation the specimen canundergo, rather than the pressure applied. For instance, on the smallerdiameter samples it again took between 150 and 200 lbs of compressiveload before the sample failed. For the smaller sample this equates tomore than twice the pressure at failure than the larger sample, but bothsamples appeared to fail at approximately the same percent reduction inheight.

Example 6

In addition to compressive loading tests, two 6 inch long synthetic rockcores with fractures tapering from 4.5 mm to 1.5 mm were packed with theH₂ZERO/FLEXPLUG OBM slurry containing a mixture of STEELSEAL FINE andBARACARB 600 products as the packing agent, Table 7. BDF-391 and BDF-393are lost circulation additives with a d50 particle size distribution ofapproximately 725 and 1125 microns respectively. The d50 particle sizedistribution specifies a size for which 50% of the total volume ofparticles is smaller in size than the value. Packing agent particulateswere added to achieve an 80 ppb loading. STEELSEAL FINE lost circulationadditive is a resilient graphite material commercially available fromHalliburton Energy Services. BARACARB 600 bridging agent is a sizedcalcium carbonate commercially available from Halliburton EnergyServices. TABLE 7 Liquid Volume Solid Material (cc) Weight (g) Water 113HZ-10 75 HZ-20 26 FLEXPLUG OBM lost circulation material 65 BDF-391 6BDF-393 17 BARACARB 600 bridging agent 29 STEELSEAL FINE lostcirculation additive 8

The cores were packed in the Extrusion Rheometer on a Tinius-Olsenmachine. Both cores were packed at a pressure of approximately 280 psi.The cores were then heated in a water-bath at 190° F. overnight. Eachcore was then placed in the Hassler sleeve Dislodgment Apparatus andpressured until the fracture plug failed. The first core dislodged at820 psi and the second dislodged at 640 psi. In comparison, FLEXPLUG OBMlost circulation material tends to fail at pressures of 150 psi or lessin this same fracture geometry.

Example 7

Filler materials other than FLEXPLUG OBM drymix lost circulationmaterial were used to produce slurries similar to that listed in Table 4for the purpose of qualitative comparison of such discernablecharacteristics as flexibility, gel time and firmness. The fillersinvestigated, and the relative rating of the resultant productcharacteristics are listed in Table 8. FLEXPLUG OBM drymix appeared toproduce the most favorable end product due to its extreme flexibility,durability, resilience and tackiness. FLEXPLUG W lost circulationmaterial is a sealing composition, FLY ASH retarder is a coal combustionproduct, CAL SEAL gypsum additive is a gypsum cement, FDP-C661-02additive and FDP-C661VA-02 accelerating component are compressivestrength accelerants, all of which are commercially available fromHalliburton Energy Services. BAROID weighting material is bariumsulfate, which is commercially available from Baroid Industrial DrillingProducts a Halliburton Energy Services company. FLEXPLUG OBM lostcirculation material was the only filler tested that produced an endproduct with an appreciable “tackiness.” TABLE 8 Filler Gel TimeFlexibility Strength FLEXPLUG OBM lost circulation Excellent ExcellentGood material FLEXPLUG W lost circulation Excellent Excellent Goodmaterial FDP-C661-02 additive Excellent Fair Fair FDP-C661VA-02accelerating Excellent Good Excellent component BAROID weightingmaterial Excellent Fair to Poor Fair FLY ASH retarder Excellent FairExcellent CAL SEAL gypsum additive Poor Fair Good

Example 8

Several traditional particulate packing agent products were used toproduce slurries similar to that listed in Table 4 for the purpose ofqualitative comparison of such discernable characteristics asflexibility, gel time and firmness. HYDROPLUG lost circulation plug is aself-expanding lost circulation material commercially available fromHalliburton Energy Services. For each packing agent or packing material,the slurry recipe listed in Table 4 was loaded to an equivalent of 80ppb of the packing agent. Table 9 lists the observations of the finalproducts with these various packing agents. Packing quality wasdetermined by how distinct (segregated) the pack layer was. If thepacking agent remained dispersed it was given a Fair rating where apacking agent that created a thick, delineated packing layer was givenan excellent rating. TABLE 9 Packing Packing Material Tackiness FirmnessQuality BARACARB 600 bridging agent Good Fair Excellent HYDROPLUG lostcirculation plug Fair Good Good STEELSEAL lost circulation Fair GoodGood addditive FLEXPLUG OBM lost circulation Excellent Fair Poormaterial

Example 9

A base slurry as described in Tables 2 and 4 was prepared. To this baseslurry, 100 g of SANDWEDGE conductivity enhancement system coated gravelwas added as the packing agent. The resultant material displayedenhanced resiliency and flexibility when compared to the compositionwithout the resin-coated gravel.

It has been found that by adding the filler FLEXPLUG OBM lostcirculation material drymix to the crosslinkable polymer system H₂ZEROservice providing conformance control system in combination with any oneof a number of particulate packing agent products, a highly flexible,durable and adhesive product is formed. This product, via theparticulate packing agent, provides an immediate short-term plug so thatthe driller can continue to drill ahead. In addition, the thermallyactivated FLEXPLUG/H₂ZERO gel produces a long-term plug that alsocreates a limited invasion zone within the matrix of the nearby rock,creating a greatly reduced permeability zone to further strengthen theplug

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). Use of theterm “optionally” with respect to any element of a claim is intended tomean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The discussion of a reference herein is not an admission that it isprior art to the present invention, especially any reference that mayhave a publication date after the priority date of this application. Thedisclosures of all patents, patent applications, and publications citedherein are hereby incorporated by reference, to the extent that theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

1. A method of servicing a wellbore in contact with a subterraneanformation, comprising: placing a wellbore servicing fluid comprising acrosslinkable polymer system and a filler into a lost circulation zonewithin the wellbore.
 2. The method of claim 1, wherein the crosslinkablepolymer system comprises a water soluble copolymer of a non-acidicethylenically unsaturated polar monomer and a copolymerizableethylenically unsaturated ester; a water soluble terpolymer ortetrapolymer of an ethylenically unsaturated polar monomer, anethylenically unsaturated ester, and a monomer selected fromacrylamide-2-methylpropane sulfonic acid, N-vinylpyrrolidone, or both;or combinations thereof; and wherein the crosslinking agent comprises apolyalkyleneimine, a polyfunctional aliphatic amine, an aralkylamine, aheteroaralkylamine, or combinations thereof.
 3. The method of claim 1,wherein the crosslinkable polymer system comprises a copolymer ofacrylamide and t-butyl acrylate and the crosslinking agent comprisespolyethylene imine.
 4. The method of claim 1 wherein the crosslinkablepolymer system is thermally activated.
 5. The method of claim 4 whereinthe thermal activation occurs from about 180° F. to about 320° F.
 6. Themethod of claim 1 wherein the crosslinkable polymer system is present inan amount of from about 35% to about 90% by volume.
 7. The method ofclaim 1 wherein the crosslinkable polymer system forms a viscous gel infrom about 60 mins to about 300 mins.
 8. The method of claim 1 whereinthe filler comprises alkyl quaternary ammonium montmorillonite,bentonite, zeolites, barite, fly ash, calcium sulfate, or combinationsthereof.
 9. The method of claim 3 wherein the filler comprises alkylquaternary ammonium montmorillonite.
 10. The method of claim 1 whereinthe filler has a pH of from about 3 to about
 10. 11. The method of claim1, wherein the filler comprises a hydratable polymer, an organophilicclay, a water-swellable clay, or combinations thereof.
 12. The method ofclaim 1 wherein the filler has a specific gravity of from less thanabout 1 to about
 5. 13. The method of claim 1 wherein the filler ispresent in an amount of from about 8% to about 40% by volume.
 14. Themethod of claim 1 further comprising a packing agent.
 15. The method ofclaim 14 wherein the packing agent is a resilient material, a fibrousmaterial, a flaky material, a granular material, or combinationsthereof.
 16. The method of claim 14 wherein the packing agent is a resincoated particulate.
 17. The method of claim 14 wherein the packing agentis present in an amount of from about 1% to about 10% by volume.
 18. Themethod of claim 1 wherein the wellbore servicing fluid is placed as asingle stream into the subterranean formation.
 19. A method of blockingthe flow of fluid through a lost circulation zone in a subterraneanformation comprising: (a) placing a first composition comprising apacking agent into the lost circulation zone; (b) placing a secondcomposition comprising a crosslinkable polymer system and a filler intothe lost circulation zone; and (c) allowing the compositions to set intoplace.
 20. The method of claim 19 wherein the packing agent is aresin-coated particulate, a resilient material, a fibrous material, aflaky material, a granular material, or combinations thereof.